The invention relates generally to methods for applying pressure to a gel/sensor assembly in order to improve contact between the gel and the sensor apparatus by means of increasing the force applied to the gel when bringing it into contact with the sensor. Further, the invention includes press devices and methods of use thereof. In one embodiment, the invention relates to improving the performance of a gel/sensor assembly used in a device for continually or continuously measuring the concentration of target chemical analytes present in a biological system. One important embodiment of the invention involves applying a force to a collection assembly when bringing it into contact with a sensor/electrode assembly before use in a transdermal monitoring device. The present invention describes that using pressure to improve the interfacial contact between a gel and a sensor substantially increases the sensitivity of the detection system, both in the speed of recovery and overall signal measured.
A number of diagnostic tests are routinely performed on humans to evaluate the amount or existence of substances present in blood or other body fluids (including, but not limited to, urine, stool, saliva, and tears). These diagnostic tests typically rely on physiological fluid samples removed from a subject, either using a syringe or by pricking the skin. One particular diagnostic test entails self-monitoring of blood glucose levels by diabetics.
Diabetes is a major health concern, and treatment of the more severe form of the condition, Type I (insulin-dependent) diabetes, requires one or more insulin injections per day. Insulin controls utilization of glucose or sugar in the blood and prevents hyperglycemia which, if left uncorrected, can lead to ketosis. On the other hand, improper administration of insulin therapy can result in hypoglycemic episodes, which can cause coma and death. Hyperglycemia in diabetics has been correlated with several long-term effects of diabetes, such as heart disease, atherosclerosis, blindness, stroke, hypertension and kidney failure.
The value of frequent monitoring of blood glucose as a means to avoid or at least minimize the complications of Type I diabetes is well established. Patients with Type II (non-insulin-dependent) diabetes can also benefit from blood glucose monitoring in the control of their condition by way of diet and exercise.
Conventional blood glucose monitoring methods generally require the drawing of a blood sample (e.g., by finger prick) for each test, and a determination of the glucose level using an instrument that reads glucose concentrations by electrochemical or calorimetric methods. Type I diabetics should obtain several finger prick blood glucose measurements each day in order to maintain tight glycemic control. However, the pain and inconvenience associated with this blood sampling, along with the fear of hypoglycemia, has led to poor patient compliance, despite strong evidence that tight control dramatically reduces long-term diabetic complications. In fact, these considerations can often lead to an abatement of the monitoring process by the diabetic. See, e.g., The Diabetes Control and Complications Trial Research Group (1993) New Engl. J. Med. 329:977-1036.
In addition, U.S. Pat. No. 5,279,543 to Glikfeld et al. describes the use of iontophoresis to noninvasively sample a substance through skin into a receptacle on the skin surface. Glikfeld teaches that this sampling procedure can be coupled with a glucose-specific biosensor or glucose-specific electrodes in order to monitor blood glucose.
Tamada (U.S. Pat. No. 5,771,890, Jun. 30, 1998) teaches a device and method for sampling of substances using alternating polarity. A method for sampling of a substance from a subject is disclosed, as well as, a device for such sampling.
Further, Kurnik, et al., (U.S. Pat. No. 5,735,273, Apr. 7, 1998) disclose a chemical signal-impermeable mask positioned in the electrolyte flow, such that the mask is between a source of chemical signal and a working electrode which senses the chemical signal transported from the source. The patent teaches that by substantially reducing edge effects created by radial transport of chemical signal, it is possible to obtain more accurate measurement of the amount of chemical signal that is transported from a given area of source material.
In one embodiment, the present invention is directed to a press device to apply mechanical force to improve contact between an ionically conductive gel and a sensor. The device comprises: a first surface on which the gel and sensor are placed, wherein typically the first surface is conformed to hold (or substantially immobilize) a gel and sensor assembly; and a second surface which is conformed to contact the assembly such that the application of mechanical force to the first and second surfaces of the device brings the gel into contact with the sensor, wherein the amount of mechanical force that can be applied is lower than the amount of force that would cause unacceptable deformation of the gel, sensor, or assembly.
In another embodiment, the invention is directed to a method of improving signal detection in a transdermal sampling device having an ionically conductive material in contact with a sensor. The method comprises applying force to bring the tonically conductive material into contact with the sensor, where the amount of force applied is lower than the amount of force that would cause unacceptable damage to the conductive material or sensor.
In an alternative embodiment, the force is applied via mechanical pressure, and the mechanical pressure is applied by a press device as described above.
The methods and devices of the present invention are useful for any sensor application in which the sensor response is limited by inadequate interfacial contact between components (for example, an ionically conductive material (e.g., a gel) and a sensor).
The present invention describes using pressure to improve the interfacial contact between a gel and a sensor, thus substantially increasing the sensitivity of the detection system, both in the speed of recovery and overall signal measured.
These and other embodiments of the subject invention will readily occur to those of skill in the art in light of the disclosure herein.